There was a 16-year gap between the 1990 release of Final Fantasy III on Famicom and its 2006 remake on Nintendo DS, and a 31-year gap before the Pixel Remaster brought something more akin to the original game to a new platform.
That might be because the original game's legendary programmer was so good nobody could replicate his code. That programmer is Nasir Gebelli, an Iranian-born man with royal ties who moved to the US to study computer science and avoid the 1979 Iranian Revolution.
His early games were legendary among PC enthusiasts of the time, to the point where Doom co-creator John Romero once called him "my number one programming god, my idol." Nasir - the name by which he was typically credited in his games - eventually began to work with Squaresoft, first on games like 3-D Worldrunner and Rad Racer before programming the first three entries in the Final Fantasy series.
Final Fantasy 1 and 2 would enjoy numerous ports and remakes for other platforms in the years that followed, but it wasn't until 2006 that Final Fantasy 3 ended up on another platform, and it wouldn't be until 2021 that the Pixel Remaster brought the original game to a new audience.
According to an article from Japanese outlet MagMix, translated by Automaton West, Nasir's programming skills might just be the reason for that gap.